Off-reef food can complement diet of fishes at bleached reefs

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Off-reef food can complement diet of fishes at bleached reefs

April 27, 2019 - 20:25
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For the fishes at coral reefs, how reliant are they on outside food that enter into their environment? If the corals at their reef are bleached, would they be in danger of starvation?

Reef fishes at Papahānaumokuākea Marine National Monument.

Reef fishes don't just rely on the coral reef environment to provide them with food. Food, in the form of plankton, also enter the reef environment due to ocean currents and tides; this forms another food source for reef fishes.

However, if the corals are bleached, they are unable to provide food and this means a reduced food source for reef fishes. Researchers from the ARC Centre of Excellence for Coral Reef Studies at James Cook University sought to find out how reliant the fish at coral reefs are on outside food sources.

Using high-resolution surveys and individual biomass production estimates, PhD candidate Renato Morais and Professor David Bellwood generated the first map that shows where the energy comes from for all fish on a coral reef. More than 18,000 fish from over 300 species were covered in the study.

They discovered that “for many reefs, food from outside can sustain fish populations, even when the coral is badly damaged.”

According to the press release, “for every kilogram of fish produced on the reef, more than 400 grams of that kilogram relied on food derived from the open ocean, rather than the reef itself.”

In addition, for the side of the reef facing the open ocean, the number rises to nearly 600 grams.

Their findings, published in the Current Biology journal, is promising news for bleached coral reefs.

“The discovery that reef fish get so much of their food from off-reef sources was encouraging, especially because many species that feed on oceanic material have a history of disappearing after coral loss,” said Morais.

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